WASHINGTON • In 1974, the paleoanthropologist Donald C. Johanson led an expedition to Ethiopia to look for fossils of ancient human relatives.
In an expanse of arid badlands, he spotted an arm bone. Then, in the area surrounding it, Dr Johanson and his colleagues found hundreds of other skeletal fragments.
The fossils turned out to have come from a single 1m-tall female who lived 3.2 million years ago. The scientists named her species Australopithecus afarensis, and the skeleton was dubbed Lucy.
Lucy remains one of the most famous discoveries in paleontology. Her death, however, has been a mystery. Now, after poring over the celebrated bones, a team of scientists has concluded that Lucy died most unceremoniously: killed by a long fall out of a tree.
The new study, published on Monday in the journal Nature, came about because Lucy's skeleton - normally housed at the National Museum of Ethiopia - was taken on a tour of the US in 2007.
Lucy spent 10 days at the University of Texas at Austin, where scientists put her bones through a CT scanner.
"We just decided, by golly, we were going to scan every little bit of Lucy because it may never be done again," said Dr John Kappelman, a paleoanthropologist at the university.
Since then, he and his colleagues have turned the scans into 3D models, piecing together virtual fragments to get a more accurate idea of their original shapes. Last December, he noticed a puzzling break in Lucy's upper right arm.
He also observed more compressive fractures, and so-called greenstick fractures, in which a bone cracks only on one side, much like what happens when a living tree branch breaks. Both kinds of fractures can happen during falls.
Dr Kappelman and his colleagues believe Lucy must have fallen from a tree. They base that conclusion on what geologists have determined about the environment where she lived: At the time, it was a low-lying wooded area around a stream, with no cliffs nearby.
Her injuries suggested "she stretched out her arms at the moment of impact in an attempt to break her fall", said Dr Kappelman.
NEW YORK TIMES, AGENCE FRANCE-PRESSE